Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$134.84	5.786%	$142.6418	$142.64	$142.65	$142.60
Purchase #2	$39.76	3.737%	$41.2458	$41.25	$41.25	$41.20
Purchase #3	$175.47	6.731%	$187.2809	$187.28	$187.30	$187.30
Purchase #4	$68.51	12.685%	$77.2005	$77.20	$77.20	$77.20
Purchase #5	$168.54	11.774%	$188.3839	$188.38	$188.40	$188.40
Purchase #6	$79.38	7.493%	$85.3279	$85.33	$85.35	$85.30
Purchase #7	$142.95	3.754%	$148.3163	$148.32	$148.30	$148.30
7 purchase totals =	$809.45		$870.3971	$870.40	$870.45	$870.30